Functional Neuroanatomy & Neurological Bases of Cognition

Nigel Schofield, Consultant Clinical Neuropsychologist May 2008

Evolutionary Development

• If you examine the brain in an evolutionary perspective, this can help to understand the interlinks between form and function. The brain can be divided anatomically and functionally into three basic components.

Reptilian Brain

• Corresponds to the brainstem• Consists of the medulla, pons,

midbrain and basal ganglia• Not only responsible for vegetative

functions but also for many volitional behaviours directed towards individual preservation and propagation such as feeding, drinking and sexual aggression.

Paleomammalian Brain

• The primitive cortex of the limbic lobe

• Subserves primitive (but distinctly mammalian behaviours) such as hoarding and parental care of offspring.

Neomammalian Brain

• The neocortex

• Subserves higher cognitive functioning and speech which facilitate social behaviour.

                       

 

Lurias Work

• Simple anatomical localisation of function does not explain cognitive and behavioural complexity.

• Postulated three functional units

Luria’s 3 Functional Units

• Motor unit – regulates motor tone

• Sensory unit – receives, processes and stores sensory information

• The unit for programming, regulating and verifying action

How do the units work?

• Progression from sensation through to symbolic function in each unit

• Primary, secondary and tertiary areas

e.g. Damage to the Visual Parts of the Sensory Unit

• Primary areas – losses of parts of the visual field

• Secondary areas – may lead to poor judgement of motion, poor distance judgement, impaired colour perception

• Tertiary areas – could lead to visual object agnosia

e.g. Damage in the Speech Pathways of the Motor Unit

• Primary areas – dysarthria

• Secondary areas – dysphasia

• Tertiary areas – poor speech spontaneity

Weaknesses of Luria’s Model

Does not fully explain the integration of focal brain functions because:-

• Divisions between sensory and motor neurons sometimes not clear

• Some functions exist several in anatomically distinct areas of the brain

• There are multiple parallel functions in the brain, not simple stepwise processes

Arousal, Attention, ActivationArousal, Attention, Activation

Arousal

Major Areas of Cognition

• Attention and concentration

• Perception

• Memory

• Language

• Control of motor behaviour

• Executive function

Attention and Concentration

Three attentional networks:-• Alerting – achieving and maintaining an alert

state in preparation for incoming stimuli• Orienting – selectively focusing on one or more

items out of many candidate ones• Executive control – monitoring and resolving

conflicts in planning, error detection and overcoming habitual actions

• All dependent on the brain being “aroused”

Localisation of Attentional Networks

• Alerting – frontal and parietal cortical regions particularly of the right hemisphere

• Orienting – parts of the superior and inferior parietal lobe, frontal eye fields and subcortical areas such as superior colliculus of the midbrain, and pulvinar and reticulate nucleus of the thalamus

• Executive control – includes midline frontal areas(especially anterior cingulate and lateral prefrontal cortex) and the basal ganglia

3 Compartments of Attention

Top-down modulation from prefrontal, parietal & limbic cortices

Bottom-up modulation from ascendingreticular activating system

Modality & domain specific attentionalmodulations ( sounds, tactile stimuli,

colours, motion, words, spatial targets,faces, objects, memories etc.)

Components of the ARAS• Reticulothalamic cortical pathway – promotes and

maintains cortical arousal by facilitating transthalamic passage of sensory material towards the cortex.

• Transmitter specific pathways originating in the brainstem or basal forebrain, and projecting to the cerebral cortex – include dopaminergic projections from the raphe nucleus & noradrenergic projections from the locus coeruleus of the brainstem, and cholinergic & gabaminergic pathways originating in the nucelus basalis.

Limbic elements of attention• Anterior cingulate cortex plays a core pivotal

role in attention – bilateral damage gives rise to akinetic mutism

• Intralaminar nuclei of the thalamus receive inputs from the brainstem nuclei and relay info widely to the cortex, with a reciprocal feedback loop from the cortex modulating these ascending pathways via the thalamus

Cortical elements of attention

• Parietal cortex involved in sustained and selective attention

• Dorsolateral prefrontal cortex has a key role in divided attention

Perception

How we take energy from

the environment & convert it into

a representation that the mind

can use

Perceptual Problems• Visual field cuts• Cortical blindness• Achromatopsia – inability to discriminate

between colours (medial occipito-temporal)• Hemianaesthesia• Hemineglect – ? an attentional problem• Hemispatial neglect • Hemiakinesia• Agnosias• Loss of taste and/ or smell

Types of Agnosia

• Visual agnosias – inability to recognise familiar objects e.g.– Prosopagnosia – inability to recognise faces– Agnostic alexia – inability to read– Colour agnosia – inability to retrieve colour

information e.g. what colour are bananas– Object agnosia – inability to name objects– Simultiagnosia – inability to recognise a whole

image although individual details are recognised

• Auditory agnosia – an inability to recognise auditory stimuli

- Auditory/verbal information agnosia – an

inability to hear words- Auditory agnosia – inability to hear

environmental sounds e.g. car starting or dog barking

- Receptive amusia – inability to hear music• Somatosensory agnosia (Astereognosis or tactile

agnosia)

- Difficulty perceiving objects by touch

Object recog, understanding & namingFunctions Object Consequence of impairment

Discrimination of Apperceptual agnosia

shape, colour, location

Perceptual classification Associative agnosia

(modality specific)

Knowledge of objects Associative agnosia

(non-modality specific)

Store of names Anomia & paraphasias

Spoken name

Visual analysis

Object recog.

Semantic system

Lexicon

Apperceptive vs Associative Agnosia

Basic High-level Naming Semantic

visual perceptual & knowledge

proc analysis identific.

Apperc. / x x /

Assoc. / / x x /

Prosopagnosia Face

Voice, gait etc.

Spoken name

Visual analysis

Expression, lip reading,Feature matching

Face-recognition units****

Semantic systemKnowledge of person

Lexicon of names

Topographical Disorientation

• Egocentric disorientation – an inability to represent the location of objects relative to self (often seen in conjunction with features of Balints syndrome – due to bilateral posterior parietal damage

• Landmark agnosia – an inability to recognise salient environmental stimuli (buildings etc) – a form of associative agnosia due to lingual gyrus (basal occipital) damage

• Anterograde spatial disorientation – an inability to create “new maps” or representaions of the environment – due to damage to the right parahippocampal gyrus

Memory Taxonomy

CorticalNetworkMemory

Basic Neuroanatomy of MemoryA) Subcortical structures• Basal ganglia and cerebellum – Procedural

memory. Caudate nucleus involved particularly with habit formation (unconscious learning)

• Thalamus – Temporal sequencing information. Also supplementary role to medial temporal lobes in new learning

• Basal forebrain – The binding together of different modal components in episodic memory

B. Cortical structures• Hippocampus – Acquisition of new factual

knowledge• Primary association cortex – Visual, auditory and

somatosensory data• Non-medial temporal – Retrieval of previously

learned material e.g. autobiographical info, names, faces

• Ventromedial frontal lobes – Memory traces linking facts and emotion

• Dorsolateral frontal lobes – Recency and frequency memory. Working memory

Limbic System Elements of Episodic Memory

Frontal Lobe Retrosplenial Cortex

ThalamusAnterior mediodorsal

Mamillary bodyBasal forebrain

AmygdalaHippocampus

Entorhinal cortex

Cingulate cortex

Fornix

Pre-motor cortex Sensorimotor cortex

Perisylvian cortex

Occipeto-temporal parietal junction Middle temporal gyrus Anterior temporal cortex

Posterior ventral occipetal Posterior temporal/inferior temporal cortex parietal cortex

Action Touch

Sound

Words

Motion

Colour

Shape

SemanticRepresentation

Semantic Memory

Language Areas of the Brain

Language Functions• Phonology – production & comprehension of

appropriately sequenced speech sounds (phonemes) – left superior temporal lobe and anterior insula

• Semantics –Assignment of meaning to words and production of linguistically appropriate individual words – Anterior and inferior temporal lobe (semantic representations) and Wernicke’s area (mapping sound to underlying representations)

• Syntax – Assembly of strings of words into sentences using pronouns, prepositions, tenses etc. – Broca’s area

• Prosody – Fine tuning by intonation, cadence etc – Left anterior hemisphere and basal ganglia & Emotional expression – Right hemisphere

Characteristics of Different Types of Aphasia

Type Fluent Repetition Comprehension Naming Right-sided Sensory

hemiplegia deficits

Broca no poor good poor yes few

Wernicke yes poor poor poor no some

Conduction yes poor good poor no some

Global no poor poor poor yes yes

Transcortical yes good poor poor some yes

sensory

Transcortical no good good poor some no

motor

Transcortical no good poor poor some yes

mixed

Anomia yes good good poor no no

Disorders of Reading• Peripheral dyslexias - Preserved oral and written

spelling, and ability to identify words spelt out aloud coupled with

(a) ability to write, but unable to read other than letter by letter (alexia without agraphia) – left medial occipital lobe

(b) errors reading left-hand or initial parts of words (neglect dyslexia) – Right hemisphere lesions

• Central linguistic dyslexias – linguistically based, invariably affect oral spelling

(a) Breakdown of whole word (lexical) reading, difficulty with irregularly spelt words, phonologically plausible errors (surface dyslexia) – left tempero-parietal damage

(b) Loss of sound-based (phonological) reading, semantic errors, difficulty with function and abstract words, inability to read non-words (deep dyslexia) – extensive left hemisphere damage

Disorders of Spelling• Dyspraxic dysgraphia – oral spelling intact,

defective copying – dominant parietal or frontal lobe

• Neglect dyspraxia – wide left margin or mis-spelling of initial part of words. Other neglect phenomena usually also preseent – Right hemisphere lesions

• Lexical (surface) dysgraphia – breakdown of lexical route for spelling, so

• difficulty spelling irregular words, phonologically plausible errors – left tempero-parietal damage

• Deep dysgraphia – breakdown of sound route for spelling , so semantic errors, unable to spell unfamiliar or non-words, better concrete than abstract spelling – extensive left hemisphere damage

Control of Movement

Apraxia• Limb kinetic apraxia – breakdown of fine motor

organisation of finger movements, so find it hard to copy meaningless hand movements, mimic proper gestures or use real objects flawlessly – Basal ganglia damage, supplementary motor area damage

• Ideomotor apraxia – unable to carry out motor acts to command, but often can do so spontaneously. Difficulty with selection, sequencing, spatial orientation and movements in meaningless and meaningful gestures, and demonstrating imaginary use of objects dominant lobe. Perf. improves with imitation, and real object use - Inferior parietal and prefrontal damage. Callosal lesions can impair performance of one limb (usually the left)

• Ideational or conceptual apraxia – inability to carry out a complex sequence of co-ordinated movements even though each separate component of the sequence can be successfully performed. Inability to mime use of objects, or to even use the real objects. Thus possibly a disorder of semantic memory. – Left temporal lobe damage

• Orobuccal apraxia – difficulty performing learned, skilled movements of face, lips, tongue, cheeks, larynx and pharynx on command – Inferior frontal region and insula, so commonly seen in Broca’s aphasia patinets

Frontal Executive Function• Abstract conceptual ability• Set shifting/mental flexibility• Inhibitory control• Problem solving and strategy formulation• Planning• Self-monitoring• Initiation• Sequencing of behaviour• Decision making• Temporal-order judgements• Personality, esp. drive, motivation & inhibition• Social behaviour, incl. theory of mind

Important core functions

• Controlling acquisition of new memories• Divergent thinking – choosing different

ways of approaching a situation• Environmental control of behaviour –

using cues and information from the environment to direct, control or change personal behaviour.

• Directing interpersonal behaviour

Acquisition Deficits

• Impaired working memory

• Poor associative learning – difficulty associating varying facets of memory about facts or events, thus finding it hard to make use of external cues to direct behaviour

Divergent Thinking Deficits

• Loss of spontaneous behaviour – e.g. speaking and verbal fluency decreased; decreased ability to produce graphic designs or doodling; reduced behavioural output shown by lethargy, inability to initiate

• Impaired strategy formulation and planning, especially in response to novel situations

• Poor abstract thinking e.g. concept formation

Deficits in Environmental Control of Behaviour

• Ability to inhibit responses is impaired, so perseverative on tasks

• Breaking rules and taking risks

• Unable to follow instructions

• Gambling

• Poor error perception

• Amotivation and apathy

Impaired Interpersonal Behaviours

• Inappropriate social and sexual behaviour, or altered behaviours in comparison to premorbid patterns.

• Pseudodepression

• Pseudopsychopathy

Brains are not absolutely hard-wired – as shown by these fMRI images of regional activation in different people doing a Stroop task – some overlap of dorsolateral and medial frontal lobe, inferior parietal lobule and occipital cortex plus significant other variability. There are also gender differences that can account for better gender performance on different tasks e.g. on spatial working memory tasks men have more frontal and less occipital activation, women have the opposite.